Middle Pennsylvanian (Moscovian) coal from New Brunswick, Canada: sedimentary context, organic petrography, and palynology

The Clifton Formation hosts two thin, uneconomic Middle Pennsylvanian coals associated with erect, lycopod-cast forests exposed along the southern shore of Chaleur Bay, New Brunswick, Canada. The study focuses on the depositional setting of coal and mudrock deposits, mudrock (B/Ga) geochemistry, coal geochemistry and petrography, and the palynology of the peat forest and assemblages recovered from clastic paleosols associated with beds entombing standing trees. Similar to the Minto coals, Clifton coals are high in ash and sulphur, and clastic sediments were deposited under freshwater conditions (B/Ga ratio <3). Dry, ash-free volatile-matter content averages 40.23 wt.% and sulphur content averages 10.75 wt. %. A high volatile B/C rank is confirmed with coal petrographic analyses of vitrinite where the VRomax reflectance value of the samples is 0.74. The high sulphur content is attributed to sulphate dissolution of Mississippian Windsor Group gypsum and anhydrite deposits, delivered to the incipient mires via fluvial and/or groundwater systems. Coal palynological assemblages are of low diversity and dominated by the pioneer arborescent lycopod Paralycopodites, and similar in composition to vegetation responsible for Minto peat bodies. Palynological assemblages from the Clifton coal (Unit 7) and underlying paleosol (Unit 5A) are dominated by spore-bearing plants and differ in systematic composition (Jaccard similarity coefficient 0.1) and diversity. Where evidence of woody gymnosperm and coniferous groups are absent from the coal, their presence in paleosol (Unit 5A) and suspension-load sediment deposits (Unit 7), along with a higher proportion of tree ferns, pteridosperms and sphenopsids, indicates a more complex vegetation colonized mineral soils outside of contemporaneous peat forests. The formation is assigned to the Torispora palynozone of Moscovian (Bolsovian) stage.